AdamJD

I carry a multimeter with me. When I was having these issues, I used it with the engine running to check steady voltage to the power buss at the alternator circuit breaker. That’s how I figured out it wasn’t the alternator. From there it was a matter of following the connections after the alternator circuit breaker. If the alternator wasn’t steady at 14 or so at the breaker, I would have started looking at the field wire or voltage regulator.

Ditto for checking connections. I had the same issue. Would get low volt alert on JPI and then back up to 14 in a few mins or so. Sometimes longer. Replaced the voltage regulator and that did nothing. Wish we had tested output from the VR before we replaced it. Pretty easy to do. But the mechanic was convinced it was the VR. Anyway, it wasn't until I was hearing occasional popping in the headset that we determined a loose connection somewhere. Turned out to be a loose connection between the main buss and the avionics buss. After a few turns of the screw driver, the problem was solved.

Thanks for the continued ideas. I have a jpi 830 and a mechanical primary tachometer. They both agree and the JPI is pulling rpm from the mags. So I don’t think that’s the issue. But keep the ideas coming as we are stumped. Unfortunately I had to postpone todays flight so will have to wait a few days to do more troubleshooting.

The lowest I went was 2350 when I did the go-around test at altitude. I'll try to go to 2200 and back up to 2500+ this afternoon when I fly.

That was true on my most recent flight. But the flight before that I got it to surge to ~2650 at least once by pushing hard.

Same hours on the ATH, as the hub was done with the overhaul in 2012.

That's interesting. It doesn't take much movement to make a 150 RPM difference. We will definitely have to check that out. @jetdriven, what are your thoughts? We were wrenching on it a bit and it didn't seem like any of those 6 screws were loose - but we should check them. Might explain when sometimes you push hard, the RPMs go up to near 2700. Pushing hard may be rotating the whole thing a hair.

Don’t know how to rule that out, but I checked with my mechanic this afternoon and he doesn’t seem to think it’s the prop.

Appreciate all of the thoughts. Because I had all 4 cylinders rehoned I've been running straight Phillips mineral oil and running at high MP and lower altitudes, keeping power above 75%. I usually use Aeroshell W100 when not in breakin mode. I have about 12 hours since the cylinders were put back on. The problem appeared on the second flight, right after the first 2-hour break-in flight. However, for the break-in flight, I flew the first hour at 2650, so I didn't pull the prop back. For the second hour, I flew between 2450 and 2550, so it might still have had a problem and I didn't know it. I did try a simulated go around at altitude. Low MP, Low RPM, mixture full rich. When I firewalled everything, prop surged to 2600 and then back down to 2500. So the governor regulated back to 2500 instead of keeping it above 2600 (or the prop could be sticking as takair mentioned - not sure how to test that).

I don’t use vernier for takeoff. But do use it to pull back in cruise. But after experiencing this issue, I have pushed the prop back to full in cruise without using vernier. I will say that testing on the ground didn’t make a difference vernier or not. However, not using vernier at all is a good thing to test next flight to rule it out.

Hi all, I'm hoping Mooneyspace can work its magic and help my mechanic (@jetdriven) and I solve an RPM mystery. I'm having a problem where my RPMs go to ~2670 on takeoff, which is normal or just slightly low for my '67 M20F. At altitude, I pull the RPMs back to cruise RPM of ~2450 to ~2500. After this, I can no longer get the RPMs above ~2500, no matter how far forward I push the prop. A very few times, if I push hard enough, forcing the knob closer to the firewall, the RPMs would surge up to ~2670 or so. However, most times when I pushed the knob hard, it won't go above 2500. The cable is less than two years old and is a vernier-type control from McFarlane. The cable has cushion between the panel and the knob, so it does not reach the panel at full forward, which is correct. We've thoroughly inspected the cable to governor and the arm is travelling to the stop screw at full forward. The cable is firmly secured to the governor cable bracket and is not slipping. The prop governor is a PCU5000 model ATH-1. The governor expert we talked with doesn't think it's a traditional problem with the governor and thinks if we pull it to bench test it, it will pass, as it seems to be governing oil pressure to the prop ok. Prop hub was replaced in 2012 and has approx 1100 hours. No signs of any leaks in prop. This problem didn't exist until after an annual this February where I had all 4 cylinders rehoned, which is obviously not directly related to this issue, but may be indirectly related as things were moved around for the cylinder removal and install. Has anyone experienced anything similar? If so, what was the cause / outcome? Thanks, Adam

Unrelated but funny recent story. I had work done on my throttle cable. On departure, lifted off, pull the J-bar out to raise the gear and the damn horn is going off at full throttle. I fly the plane to 1,500 and then stick my finger in the gear down block to silence the horn. My gear horn breaker is the automatic / flush kind that can't be pulled to stop the horn. So now what? Fly for hours with my finger in the hole? Turn around and land? So I crumple up a piece of paper and stick it in the gear down block hole. Upon arrival, slowed down to gear speed, took the paper out, locked the J-bar in. Landed and later explained to the newish-to-Mooneys mechanic how to adjust the micro-switch correctly.

I need to move... +1 for RPM. Just finished my second annual owning the plane. The first was done at a MSC. It was expensive, but that should have been expected for a first annual. However, there were a few things done without asking and a few things done half-assed that I should have pushed back on. First airplane ownership rookie mistake. My second and most recent annual was with RPM. Everything is explained and discussed. The base "cost" is in the 30ish hour range. It's a small business, so selfishly I hope you don't all go to Byron for a winter annual as I want to preserve my spot. But the experience was great. Right up until he removed a cylinder for a planned replacement and borescoped the cam shaft. But that's another very painful story...

@Neshi, as of a year ago, you could display multiple misc fields on the GI275 ADI. See below for a pic from a friend of mine's F. HOWEVER, I couldn't configure mine this way because I have the GFC500. The command bar for the GFC500 is the reason. I was bummed. My solution is to display TAS on the ADI, winds on the HSI, temp on the GFX345 and GS on the 430W.

Bought my first plane - an M20F 18 months ago from a private seller. I'm based part time at GAI (where I've flown for 20 years) in a tie-down and fly often. I also have a good friend and CFI based at CGE, but not a Mooney CFI. I did my transition training with a Mooney CFI out of GAI - there are several and mine was good. PM me if you want to chat about my experience through the purchase, training and maintenance. PS - One good thing about GAI is the Mooney community there. Along with RPM, there are 7 or 8 Mooney owners who actively communicate. It's a good resource of like-minded pilots and owners to share and learn from.